Ischemic heart disease (IHD) or myocardial ischemia, is a disease characterized by tissue hypoxia due to reduced blood supply to the heart muscle, usually caused by coronary artery disease. IHD is the leading cause of death and morbidity in the USA. Increase in coronary vessel diameter by vasodilatation (acute response), and increase in vessel density (delayed response) are two major defenses of myocardium from ischemic insults. While coronary vasodilatation is primarily dependent on endothelium-generated nitric oxide (NO), the increase in capillary density initially requires proliferation and migration of vascular endothelial cells (ECs). Increased levels of reactive oxygen species (ROS) are often observed in many cardiovascular diseases, including IHD, giving rise to the notion that ROS cause endothelial dysfunction. However, recent major interventional clinical trials using antioxidants (e.g. HOPE, ATBC), have largely produced negative results in reducing primary endpoints of cardiovascular death and morbidity. Reports from our lab demonstrated that reduced ROS levels inhibited signal transduction events that are essential for NO generation in the vascular endothelium and for coronary vasodilatation. Preliminary Results also showed that c-Src responds to changes in endothelial redox levels and promotes downstream Pl3K-Akt signaling, which in turn activates eNOS and inhibits the growth inhibitory transcription factor, FOXOi, in coronary vascular ECs. This application will test a novel HYPOTHESIS that conditional increase in endothelium-specific-ROS will activate c-Src-Pl3K-Akt-eN0S pathway and inhibit FOXO1, and thus, will result in coronary vasodilatation and increased vessel density in a myocardial ischemia model in vivo. Utilizing a newly developed binary transgenic mice that can induce conditional expression of Nox2 and 2-fold increase in ROS in vascular endothelium, we will determine whether EC-ROS activate c-Src-Pl3K-Akt signaling, proliferation and migration of mouse heart ECs in vitro (Aim 1); whether EC-ROS induce Pl3K-Akt-eNOS activation, NO synthesis and coronary vasodilatation (Aim 2); and whether EC-ROS increase vessel density in ischemic myocardium in an LAD ligation model in vivo (Aim 3).